Flexible rubber article and method of making

ABSTRACT

A multi-layer flexible article includes a first layer of natural rubber, a second layer of natural rubber, polyurethane, poly(acrylamide-acrylic acid, sodium salt) and polyethylene oxide and a third layer of acrylic copolymer and fluorocarbon telomer resin. The article is preferably a glove formed by the method of dipping a hand shaped mold into baths containing aqueous emulsions of the components used to form the layers. Gloves manufactured according to the method are substantially wet-hand and dry-hand donnable as compared to powdered latex gloves of similar size. The finished gloved is water washed and wet autoclaved to substantially reduce the protein content from the natural rubber and substantially remove other water extractable allergenic moieties. The washing and autoclaving renders the glove substantially hypoallergenic as compared to gloves not so treated.

This application is a divisional application under 37 C.F.R. § 1.60 ofprior application Ser. No. 08/264,588 filed on Jun. 23, 1994 now U.S.Pat. No. 5,545,451, which is a file wrapper continuation of Ser. No.07/896,642 filed on Jun. 10, 1992, now abandoned.

FIELD OF INVENTION

This invention relates to flexible rubber articles and more particularlyto rubber surgeon's gloves and the method of making same.

BACKGROUND OF THE INVENTION

Flexible surgeon's gloves have very demanding requirements. They shouldhave strength to resist tearing and should be thin and flexible to allowtouch sensitivity. Further, they should be easy to don with wet or dryhands, but not be slippery for handling instruments.

Traditionally, surgeon's gloves have been manufactured by dipping moldsor forms shaped like hands into baths containing natural rubber latexemulsions to form a film of the desired thickness. The film is thencured and the glove is removed from the mold. There are numerousproblems with the manufacture and use of natural rubber gloves, animportant one of which is the step of removal from the mold form.Removal from the mold can be difficult because the cured latex tends tobe tacky and may adhere to the mold. Further, plain natural rubber latexgloves adhere to themselves and tend to be very difficult for a surgeonto don. This is particularly true in actual use situations where asterility protocol is followed with the surgeon having wet hands.Techniques for addressing these problems have developed over the years.Initially, mold-release powders were dusted onto the surface of the moldforms to facilitate the removal of the glove from the form. Since thegloves are generally turned inside out as they are stripped from theform, these powders then aided the subsequent donning of the glove bythe surgeon.

A wide variety of powders including talc, lycopodium, calcium carbonate,starch and modified starches has been used. Problems were identifiedwith granuloma formation in patients and attributed to powders,particularly talc and its use has long been abandoned. Powdered glovesare still widely accepted today with epichlorohydrin modified starchesbeing used quite successfully as powders for gloves by carefullycontrolling the material used and the amounts present on each glove.

As an alternate to powder, there are many disclosures of coating ortreatments of gloves to modify their surface properties. These surfacemodifications have enjoyed varying degrees of success, as high qualitypowdered gloves are still considered optimum in terms of strength,tactility and ease of donning and removal.

There are two general ways of achieving natural rubber latex gloveswhich do not require powder for donning, chemical treatment of therubber surface and adding materials onto a natural rubber surface.Representative of the chemical treatment is halogenation. Halogenationrenders a rubber surface slippery, but it is most effective inconjunction with dry hands and additionally, the treatment may weakenand embrittle the overall film. It may also adversely affect the shelflife of a sterile glove.

There are many disclosures relating to adding materials to a rubbersurface to improve its slip characteristics with both wet and dry skin.Representative of the disclosures is U.S. Pat. No. 4,575,476 to Podellet al. Podell et al. teaches a dipped rubber article having a skincontacting surface layer formed of a hydrogel polymer, such as polyvinylpyrrolidone, polyhydroxyethyl acrylate or methacrylate and copolymers ofthese with each other or with acrylic or methacrylic acid, or with2-ethylhexyl acrylate or a ternary copolymer of 2-hydroxyethylmethacrylate, methacrylic acid and 2-ethylhexyl acrylate.

Gloves prepared according to the teaching of Podell et al. can be shownto have less mechanical strength and reduced resistance to acceleratedaging after sterilization compared to conventional powdered latexgloves. Under conditions of mechanical stress, such as extremeelongation as could occur during donning, they may partially delaminateand lose particles from the hydrogel coating. Further, they tend to besome what thicker than many powdered latex gloves thereby adverselyaffecting tactile sensitivity.

SUMMARY OF THE INVENTION

A multi-layer flexible article includes a first layer formed fromnatural rubber. A second layer is formed from natural rubber,polyurethane, poly(acrylamide-acrylic acid, sodium salt) andpolyethylene oxide. A third layer is formed of acrylic copolymer andfluorocarbon telomer resin.

The article preferably may be a multi-layer surgeon's glove formed bydipping a hand shaped mold form in a series of baths. The preferredgloves are wet hand and dry hand donnable without the need for powder,and have greater strength compared to existing gloves of similarthickness. The structure of the gloves substantially reduces theincidence of air pinhole defects in manufacture of the gloves whencompared to natural rubber latex gloves of similar thickness.

A method for manufacturing multi-layer articles, preferably gloves,includes dipping a hand shaped mold form in a series of baths to form onthe surface of the mold, a patient contacting first layer of naturalrubber, a wearer contacting layer of acrylic copolymer and fluorocarbontelomer and, intermediate to the wearer and patient contacting layers, alayer including natural rubber, polyurethane, poly(acrylamide-acrylicacid, sodium salt) and polyethylene oxide. The layers are washed, driedand cured to form a unitary structure, then the structure is everted asit is removed from the mold as a finished glove. The glove preferablythen has a coating of lubricant applied to the surface, preferablyfollowed by water washing, wet autoclaving and drying.

DETAILED DESCRIPTION

In accordance with the present invention, a preferred embodiment is asurgeon's glove formed on the surface of a mold. The manufacture beginswith a surface of a cleaned and coagulant treated mold form which iscoated by dipping the mold in a bath containing a natural latex rubberemulsion.

The glove molds are individual for the right and left hands. The moldsare made in a variety of sizes and shapes corresponding to the varioushand sizes for which the gloves are intended. The molds are preferablymade of ceramic, most preferably porcelain, bisque or glazed, but othermaterials such as stainless steel, glass, hard woods and plastic mayalso be used.

Suitable coagulants include, but are not limited to, calcium nitrate,calcium chloride, acetic acid, magnesium acetate, and the like. A bathwith an aqueous solution of about 20 to 25%, preferably 22.5%, calciumchloride with about 0.1 to 0.2% octoxynol, preferably 0.15%, ispreferred for coating the molds with coagulant.

When the mold is dipped in the latex bath, the latex forms a patientcontacting film on the surface of the coagulant coated mold which servesas a substrate for subsequent layers. The thickness of the substratefilm and the subsequently applied layers is generally governed by thesolids content of the emulsions, the quantity of the coagulant depositedon the mold, the temperature of the mold and the residence time of themold in the baths.

In a preferred embodiment, where the substrate is formed from naturalrubber latex, the porcelain molds are cleaned in a bath with aqueoussodium hypochlorite of concentration about 2.5 to 5%, preferably 3.0%,then rinsed with 120° to 150° F., preferably 135° F., water and allowedto drain. The rinsed and drained molds are then dipped in the calciumchloride coagulant bath with a temperature preferably about 110° to 130°F., most preferably 120° F. The molds with the coagulant on theirsurface are dried at about 210° to 270° F. for about 8 to 10 minutes,preferably 250° F. for 8.5 minutes, then dipped into a bath containingan aqueous anionic natural rubber latex emulsion.

The latex bath has a total solids content preferably about 25 to 35%,most preferably 30%, a temperature of preferably about 75° to 90° F.,most preferably 82° F., and a pH about 9.5 to 10.6, most preferably,10.1. The mold remains in the bath preferably about 20 to 30 seconds,most preferably 25 seconds, and is then removed, and preferably aminimum of 25 seconds is allowed for the latex film to gel. This formsthe substrate layer.

The mold with the substrate layer on its surface is now dipped into asecond bath containing an aqueous emulsion of anionic natural rubberlatex, polyurethane latex, poly(acrylamide-acrylic acid, sodium salt)and polyethylene oxide. The total solids content of the bath ispreferably about 13 to 15%, most preferably 14%, at a temperaturepreferably about 75° to 90° F., most preferably 82°, and a pH preferablyabout 7 to 10, most preferably 9. The proportions in parts per hundredof the components of the bath are anionic natural rubber latex,preferably 16 to 18, most preferably 17, polyurethane latex, preferably11 to 13, most preferably 12, poly(acrylamide-acrylic acid, sodium salt)(10% carboxylic), preferably 0.35 to 0.43, most preferably 0.39,polyethylene oxide, preferably 0.26 to 0.32, most preferably 0.29, andwater, preferably 69 to 71, most preferably 70. The mold is in the bathpreferably about 25 to 45 seconds, most preferably 36, is then removedfrom the bath and dried, preferably about 160° to 200° F., mostpreferably, 180° F., preferably about 160 to 180 seconds, mostpreferably 180 seconds. This forms the intermediate layer.

Following the formation of the intermediate layer over the substratelayer on the surface of the mold, the mold with the layers on itssurface is spray washed, preferably about 10 to 20 minutes, mostpreferably 15 minutes, preferably with 120° to 150° F., most preferably130° F., water, then air dried preferably about 1 to 3 minutes, mostpreferably 2.5 minutes, preferably about 200° F.

After drying, the washed and dried mold with the layers on its surfacehas a wearer contacting layer applied over the intermediate layer bydipping the mold into a third bath containing an aqueous emulsion ofacrylic copolymer and fluorocarbon telomer resin. The bath has a totalsolids content preferably about 2 to 3%, most preferably 2.5%, and acomposition in parts per hundred of acrylic copolymer preferably about1.41 to 1.88, most preferably 1.65, fluorocarbon telomer resinpreferably about 34 to 38, most preferably 36, and water, preferablyabout 60 to 65, most preferably 62.35. The bath has a pH preferablyabout 6.5 to 9, most preferably 7.3. After dipping, the mold remains inthe bath preferably 25 to 45 seconds, most preferably 36 seconds, thenis withdrawn. The mold with the layers on its surface is then dried andcured preferably about 40 to 50 minutes, most preferably 44 minutes,preferably about 215° to 235° F., most preferably 225° F. This dryingand curing step causes the layers to form a unitary structure andcompletes the formation of a glove.

The gloves are then stripped from the molds by everting them, having theeffect of placing the last formed wearer layer on the inside.Preferably, the gloves are further treated by tumbling with a lubricant,preferably lanolin alkoxy ether, lanolin oil alkoxy ether, fluorocarbontelomer, silicone and the like, most preferably polydimethylsiloxane,preferably about 12 to 18 minutes, most preferably 15 minutes,preferably at 140° to 160° F., most preferably 150° F. to apply acoating of the lubricant to the surface.

Following the silicone treatment, the gloves are preferably water washedand subjected to a wet autoclaving cycle, preferably for 12 to 18minutes, most preferably 15 minutes, preferably with a peak temperatureabout 200° to 300° F., most preferably 250° F., then tumble driedpreferably about 20 to 30 minutes about 140° to 160° F., most preferably30 minutes and 150° F.

Natural rubber latex is known to have a protein component, which isbelieved to be responsible for some allergic reactions to articlesformed from natural rubber. The water washing and wet autoclaving stepsfollowed by drying produce a significant reduction in the proteincomponent as well as substantially reducing any other water extractableallergenic moieties present compared to gloves not so treated and othercommercial surgeon's gloves. The protein content was determined by theBradford test, a widely used method for protein quantitation. There aremany reports in the recent literature attributing allergic reactions,and, in some cases, anaphylaxis, to the proteins present in naturalrubber latex. The instant invention's wet autoclaving step is believedto substantially remove and denature these proteins. A comparison usingthe Bradford test for protein level was made between gloves of theinstant invention and known commercially available gloves intended forsimilar applications.

    ______________________________________                                        Protein Content                                                               (ug/g of glove)   Glove                                                       ______________________________________                                        5.7               Instant Invention                                           117.0             Surgikos MicroTouch                                         85.1              Baxter Triflex                                              ______________________________________                                    

The ability of a material to cause irritation has historically beenmeasured by the degree of irritation to rabbit eyes. Recent efforts toreduce the use of animals for this type of testing has led to thedevelopment of in vitro bacteria based tests. A test which has showngood correlation to the in vivo rabbit eye test for irritation potentialis the luminescent bacterial toxicity test, provided under the tradename of Microtox. As shown in the table, the effective concentration(EC₅₀) is the weight of glove material in milligrams per 1000milliliters of extraction medium required to reduce the light output ofluminescent bacteria by 50%. The larger the number, the less cytotoxicthe material. A comparison using the Microtox test between gloves of theinstant invention and gloves produced under U.S. Pat. No. 4,575,476shows that the irritation potential of the instant invention issignificantly less.

    ______________________________________                                        Bioluminescence (EC.sub.50)                                                                        Glove                                                    ______________________________________                                        37,000               Instant Invention                                        2,568                U.S. 4,575,476                                           ______________________________________                                    

Gloves manufactured according to the above described method aresubstantially wet hand and dry hand donnable when compared to powderednatural rubber latex gloves of equivalent thickness and design. Theintermediate layer and the wearer contacting layer applied to a naturalrubber substrate can be used to impart a wet-slip and a dry-slipproperty to articles other than gloves as desired. When the coatinglayers are coupled with the water washing and wet autoclaving processsteps, the detectable protein level from the natural rubber may besubstantially reduced. Further, the concentration of any other waterextractable moieties having allergenic potential present in the articlemay be substantially reduced.

The use of rubber gloves in medical practice has taken on addedimportance with the concern about Human Immunodeficiency Virus (HIV).The strength of a glove is an important consideration to users. Theinstant invention of a multi-layer glove surprisingly provides astatistically significantly higher tensile strength and tear strengthcompared to gloves manufactured according to the U.S. Pat. No.4,575,476. This improved strength is particularly surprising because thegloves of the instant invention are stronger even when their thicknessis less than those produced under the U.S. Pat. No. 4,575,476, a widelyaccepted powder-free glove. A comparison of physical properties ispresented below using 30 samples for the instant invention and 20samples of gloves produced under U.S. Pat. No. 4,575,476. The testvalues and standard deviation for the values are shown.

    ______________________________________                                        Comparison of Physical Properties                                             (ASTM D3577-88, D412, D624)                                                              Instant Invention                                                                          US 4,575,476                                          ______________________________________                                        Tensile, PSI 4301      (240)    3730   (407)                                  Tear, PLI    346       (44)     257    (39)                                   % Elongation 903       (42)     898    (33)                                   Modulus at   548       (24)     425    (43)                                   500% Elongation, PSI                                                          Thickness (Mils)                                                              Finger       8.2                10.9                                          Palm         8.7                9.7                                           Cuff         8.4                9.3                                           ______________________________________                                    

The property of high strength coupled with reduced thickness resulted inthe glove being rated acceptable or better for tactile sensitivity by91% of users in a controlled use multi-site study in comparison to otherpremium quality surgical gloves, both powdered and powder-free. Thegloves manufactured according to the instant invention preferably have apatient contacting layer about 0.05 to 0.45 mm thick, more preferably0.15 to 0.30 mm, an intermediate layer about 0.005 to 0.20 mm thick,more preferably 0.013 to 0.05 mm and a wearer contacting layer about0.0005 to 0.05 mm thick, more preferably 0.001 to 0.005 mm.

Another benefit of the instant invention is a reduced incidence of the"air pinhole" defect experienced in glove manufacture. In a well-runglove manufacturing operation, it is generally recognized that there issome running level of various defects. A defect level of about four perone thousand gloves has historically been seen for the "air pinhole"defect for natural rubber latex gloves. Most improvements to productionprocesses are in the low percentage ranges. In the case of the instantinvention, a substantial reduction of the "air pinhole" defect isachieved. In producing the instant invention a reduction in theoccurrence of the "air pinhole" defect to below one in one thousandgloves may be achieved, thereby greatly increasing the yield for theprocess. It is believed that the application of the intermediate layerpresent in the instant multi-layer glove over the natural rubbersubstrate occludes many of the "air pinholes" present in the naturalrubber layer, thereby reducing the occurrence of the "air pinhole"defect.

A preferred method for manufacture of gloves of the present invention isshown as an example. It should be recognized that the components and theparameters presented here are to be considered exemplary of theprinciples of the invention and are not intended to limit the inventionto those components and parameters illustrated. The scope of theinvention will be measured by the appended claims and their equivalents.

EXAMPLE

Gloves of the present invention were formed by executing the followingsteps:

1) Cleaned molds by dipping in an aqueous NaOCl (3.0%) bath, removed andrinsed with 135° F., water;

2) Applied coagulant to molds by dipping in an aqueous bath, removed andair dried (8.5 min., 250° F.)

    ______________________________________                                        coagulant bath composition and conditions                                                      Parts per hundred w/w                                        ______________________________________                                        calcium chloride   22.5                                                       (Triton X-100 Rohm and Haas)                                                                     0.15                                                       water              77.35                                                      temperature 120° F.;                                                   ______________________________________                                    

3) Applied aqueous natural rubber latex to molds (substrate) by dippingin a bath for 30 seconds;

Latex Bath Composition and Conditions

Temperature 82° F.

pH 10.1

latex solids=30%;

4) Removed from latex bath and allowed to gel for 30 seconds;

5) Applied intermediate layer over substrate by dipping molds inintermediate bath for 36 seconds;

    ______________________________________                                        intermediate bath composition and conditions                                                    Parts per Hundred w/w                                       ______________________________________                                        Natural rubber latex (56% solids)                                                                 17.0                                                      Polyurethane latex (Impranil DLN;                                                                 12.0                                                      Mobay)                                                                        Polyethylene oxide   0.29                                                     Water               70                                                        Temperature         82° F.                                             pH = 9                                                                        total solids = 14%;                                                           ______________________________________                                    

6) Removed from intermediate bath and dried intermediate layer for 180seconds at 200° F.;

7) Spray washed with water for 15 minutes at 130° F.;

8) Dried for 2.5 minutes at 200° F.;

9) Applied wearer side coating by dipping molds in wearer side bath for35 seconds

    ______________________________________                                        wearer side bath composition and conditions                                                     Parts per hundred w/w                                       ______________________________________                                        Acrylic copolymer    1.65                                                     (Rhoplex HG-74; Rohm and Haas,                                                42.5%)                                                                        Fluorocarbon telomer resin                                                                        36.0                                                      (McLube 1829; McGee Ind., 5%)                                                 Water               62.35                                                     Total solids         2.5%                                                     pH = 7.3                                                                      Temperature         85° F.;                                            ______________________________________                                    

10) Air dried and cured on molds;

Time=44 minutes

Temperature 225° F.;

11) Gloves were removed from mold by everting;

12) Gloves were tumbled with silicone lubricant (polydimethyl siloxane,G.E. SM-2140), 15 minutes at 150° F.;

13) Gloves were water washed (5 min. at 180° F.) and wet autoclaved fora 15 minute cycle with a peak temperature at 250° F.; and

14) Gloves were tumbled dry in 30 minutes at 150° F.

The gloves were subsequently sorted into pairs comprising a right handand a left hand. A microorganism resistant package was formed fromsealable paper laminate, and one pair of gloves was placed into eachpackage. The package was then sealed and placed in a gamma radiationchamber for sterilization. Alternatively, packaging could be formed fromnon-woven, formed trays or the like, and sterilization could beconducted by steam, ethylene oxide or electron beam.

The process of applying a second layer and third layer, described aboveas intermediate and wearer contacting layers, has been shown to haveutility in cases where the first layer is a material other than a filmof natural rubber latex. Articles such as vinyl examination glovesformed from plastisol Polyvinylchloride (PVC) have shown benefits inpowder-free donnability and in strength when coated with theintermediate and wearer contacting layers as described in the aboveexample for natural rubber latex substrates. Additionally, the plastisolPVC gloves have also successfully been coated with just the wearercontacting layer directly by omitting the intermediate layer, therebyacquiring powder-free donnability. Other substrate films and flexiblearticles made from materials such as polyurethanes, polychloroprene,styrene/butadiene copolymer, nitrile latex and the like may benefit fromthe wet-slip and dry-slip properties imparted to articles by theapplication of the intermediate film followed by the wearer contactingcoating. These articles could include other medical devices such ascondoms, catheters and the like. Coatings of the wet-slip and dry-slipenhancing films followed by the above disclosed water washing and wetautoclaving process may also greatly reduce the reported incidences ofanaphylaxis reported with natural rubber enema probes and the like basedon the protein reduction and cytotoxicity testing reported above.

While a number of forms of the instant invention have been disclosed, itwill be understood that the invention may be utilized in other forms andenvironments, so that the purpose of the appended claims is to cover allsuch forms of devices not disclosed but which embody the inventiondisclosed herein.

What is claimed is:
 1. A process for making a flexible multilayered article comprising:forming a first layer from an aqueous emulsion comprising natural rubber latex; forming a second layer from an aqueous emulsion on said first layer comprising natural rubber latex, polyurethane, poly(acrylamide-acrylic acid, sodium salt) and polyethylene oxide; and forming a third layer from an aqueous emulsion on said second layer comprising acrylic copolymer and fluorocarbon telomer resin.
 2. The process of claim 1 wherein said aqueous emulsion for forming said first layer is a bath having about 25 to 35% total solids content and a pH about 9 to 11 comprising an anionic emulsion of natural rubber latex.
 3. The process of claim 1 wherein said aqueous emulsion for forming said second layer is a bath having about 10 to 20% total solids content and a pH about 7 to 10 comprising an anionic emulsion of natural rubber latex, an anionic emulsion of an aliphatic polyester polyurethane, poly(acrylamide/acrylic acid, sodium salt) and polyethylene oxide.
 4. The process of claim 1 wherein said aqueous emulsion for forming said third layer is a bath having about 1.5 to 4% total solids content and a pH about 7 to 10 comprising an aqueous emulsion of acrylic copolymer and fluorocarbon telomer resin.
 5. The process of claim 1 further including applying a lubricant coating selected from the group consisting of silicone, fluorocarbon telomer, lanolin oil alkoxy ethers and lanolin alkoxy ethers to at least one of a surface of said first layer and a surface of said third layer.
 6. The process of claim 1 further including water washing and autoclaving said article.
 7. The process of claim 6 wherein said water washing and autoclaving comprises a water wash for about 5 to 10 minutes at about 150° to 200° F. and a wet autoclaving cycle for about 10 to 20 minutes with a peak temperature about 180 to 280 degrees Fahrenheit which serves to substantially denature and extract proteins found in natural rubber latex and substantially remove water extractable allergenic moieties, thereby rendering said article substantially hypoallergenic compared to articles not so treated. 